1. Field of the Invention
The invention concerns compatible polymer mixtures (polymer blends) of an alkyl-substituted polystyrene as polymer component P1 and a polymer component P2 which contains carbonyl groups.
2. Discussion of the Background
As a rule, different polymer species are considered to be incompatible with one another, i.e. different polymer species generally do not form a homogeneous phase, which would be characterized by complete miscibility of the components, even down to slight amounts of a component.
Certain exceptions from this rule have caused increasing interest, particularly among the experts concerned with the theoretical interpretation of the phenomena. Completely compatible mixtures of polymers demonstrate complete solubility (miscibility) in all mixture ratios.
A summary representation of miscible polymer systems can be found, for example, in D. R. Paul et al. in Polymer & Engineering Science 18 (16) 1225-34 (1978); J. Macromol. Sci.-Rev. Macromol. Chem. C. 18 (1) 109-168 (1980) as well as in Annu. Rev. Mater. Sci., 1981, 299-319.
As evidence of the miscibility, the glass temperature Tg or the so-called "optical method" (clarity of a film poured from a homogeneous solution of the polymer mixture) is often used as a reference. (See Brandrup-Immergut, Polymer Handbook, 2nd edition, III, 211-213.) As a further test for the miscibility of polymers which are different from one another, the occurrence of the lower critical solution temperature (LCST) is used. (See DE-A 34 36 476.5 and DE-A 34 36 477.3). The occurrence of the LCST is based on the process which occurs during warming, where the polymer mixture, which has been clear and homogeneous until then, separates into phases and becomes optically cloudy to opaque. This behavior is a clear indication, according to the literature, that the original polymer mixture had consisted of a single homogeneous phase which was in equilibrium. For a further characterization of blends see also the contribution by M. T. Shaw: "Microscopy and Other Methods of Studying Blends" in Polymer Blends and Mixtures edited by D. J. Walsh, J. S. Higgins and A. Maconachie, NATO ASI Series, Series E: Applied Sciences-No. 89, p. 37-56, Martinus Nijhoff Publishers, Dordrecht/Boston/Lancester 1985. Examples of existing miscibility are represented, for example, by the systems polyvinylidene fluoride with polymethyl methacrylate (PMMA) or with polyethyl methacrylate. (U.S. Pat. Nos. 3,253,060, 3,458,391, 3,459,843). Recent results concerning "polymer blends" and possible applications for them are reported by L. M. Robeson in Polym. Engineering & Science 24 (8) 587-597 (1984).
Copolymers of styrene and maleic acid anhydride, as well as of styrene and acrylonitrile are compatible with polymethyl methacrylate (PMMA) under certain conditions (DE-A 20 24 940). The improved usage properties of molding masses of these types was emphasized. In the same way, copolymers of styrene and monomers which contain hydroxyl groups which can form hydrogen bonds with a certain composition are also compatible with polymethacrylates, for example copolymers of styrene and p-(2-hydroxylhexafluoroisopropyl) styrene (B. Y. Min and Eli M. Pearce, Organic Coating and Plastics Chemistry, 45, (1981) 58-64), or copolymers of styrene and allyl alcohol (F. Cangelosi and M. T. Shaw, Polymer Preprints (Am. Chem. Soc. Div. Polym. Chem. ) 24, (1983), 258-259). Polystyrene itself as well as other polymers which contain styrene are considered to be incompatible with polymethyl methacrylate. For example, M. T. Shaw and R. H. Somani indicate a miscibility with polystyrene of only 3.4 ppm (PMMA with a molecular weight of 160,000) or 7.5 ppm (PMMA with a molecular weight of 75,000). See Adv. Chem. Ser. 1984, 206; Polym. Blends Compos. Multiphase Syst., 33-42, (CA 101: 73 417e). Even polystyrene with a very low molecular weight has little compatibility with PMMA. For example, a mixture of 20% of a styrene oligomer with an extremely low molecular weight (MW: 3,100) still does not yield a clear product. At a molecular weight of 9,600, which is also still very low, even a solution of only 5% in PMMA is just translucent. (Raymond R. Parent and Edward V. Tompson, Journal of Polymer Science: Polymer Physics Edition, Vol. 16, 1829-1947 (1978)).
Other polymethacrylates and polyacrylates demonstrate just as little miscibility with polystyrene to form transparent plastics. This is true, e.g., for polyethyl methacrylate, polybutyl methacrylate, polyisobutyl methacrylate, polyneopentyl methacrylate, polyhexyl methacrylate and many others. See also R. H. Somani and M. T. Shaw, Macromolecules 14, 1549-1554 (1981).
An exception to this generally observed incompatibility between poly(meth)acrylate and polystyrene is reported in two recent patent applications (P 36 32 370.5 and P 36 32 369.1). According to this, polystyrene and poly-.alpha.-methyl styrene are extremely compatible with polycyclohexyl methacrylate and polycyclohexyl acrylate. The compatibility of polycyclohexyl (meth)acrylate with polystyrene and poly-.alpha.-methyl styrene is so good that compatibility between the polymer which contains styrene and the polymer which contains cyclohexyl (meth)acrylate still exists if the cyclohexyl (meth)acrylate is contained at less than 50% by weight (for example, 30% by weight) in the copolymer. In the same way, the styrene can be extensively replaced by other comonomers, without the compatibility between the polymer which contains styrene and the polymer which contains cyclohexyl (meth)acrylate being lost.
Aside from this extraordinary, complete miscibility of cyclohexyl (meth)acrylate with polystyrene and poly-.alpha.-methyl styrene, miscibility of polystyrene is only reported with polyvinyl methyl ether, polyphenylene oxide and tetramethyl bisphenol-A-polycarbonate (D. R. Paul and J. W. Barlow, J. Macromol. Sci.-Rev. Macromol. Chem., C 18 (1), 109-168 (1980)). The miscibility is generally explained by specific interactions between the different polymer species. The compatible polymer mixtures mentioned above (e.g. tetramethyl bisphenol-A-polycarbonate/polystyrene) are explained by electron donator-acceptor complex formation, for example. (See J. W. Barlow and D. R. Paul, Annu. Rev. Mater. Sci., 1981 299-319).
The majority of the compatible polymer mixtures known until now, however, are attributed to special interactions of the hydrogen bond formation type (for example, phenoxy/polyester, PVC/polyester, SAA/polyester, PC/PHFA, PVDF/PMMA. See J. W. Barlow and D. R. Paul, Annu. Rev. Mater. Sci., 1981, 303, 304).
The compatible polymer mixtures mentioned above are attributed to hydrogen bond formation or to electron donator-acceptor complex formation. The compatibility of PMMA with special copolymers of styrene and acrylonitrile or .alpha.-methyl styrene and acrylonitrile, which is found only at a certain styrene/acrylonitrile or .alpha.-methyl styrene/acrylonitrile ratio in each case, is explained by an intramolecular repulsion within the copolymer between the two comonomers styrene and acrylonitrile. This also makes it understandable that compatibility (for example between PMMA and SAN) is found only for a very specific composition of the copolymer. Since compatibility is only found for very specific comonomer ratios, this is termed "miscibility windows" (J.-L. G. Pfennig et al., Macromolecules 1985, 18, 1937-1940). Such "miscibility windows" are also reported for compatible mixtures of aliphatic polyesters and polyhydroxy ethers of bisphenol A. Here, the aliphatic polyesters are viewed as copolymers of CH.sub.x -- and COO-monomer modules. (D. R. Paul and J. W. Barlow, Polymer, 25, 487 (1984)). Paul and Barlow were able to show with this study that an exothermic miscibility can exist as a driving force for miscibility even if none of the interaction parameters are negative. The only requirement is sufficiently great repulsion energy between the comonomers of the copolymer.
Gerrit ten Brinke et al. also explain the miscibility of halogen-substituted styrene copolymers with poly-(2,6-dimethyl-1,4-phenylene oxide) (Macromolecules 1983, 16, 1827-32) with precisely this concept, and Ougizawa and Inoue, Polym. J., 18, 521-527 (1986) use it to explain the miscibility of poly(acrylonitrile co-styrene) with poly(acrylonitrile co-butadiene).
While on the one hand, the compatibility of specific copolymers with other polymers is therefore explained by intramolecular repulsion within the copolymers, thereby also explaining the "miscibility windows," specific interactions are always referred to for an interpretation of the compatibility of homopolymers (e.g. EDA complexes in the case of polyphenylene oxide/polystyrene or hydrogen bond formation in the system PVDF/PMMA). There is no overall theory to explain miscibility in a polymer, which can be used to find new compatible polymer mixtures. Such compatible polymer mixtures are sought for many applications, however.
Mechanical mixtures of polymers (polyblends) have resulted in plastic products with improved properties in certain cases and in certain areas of the plastics industry (See Kirk-Othmer 3rd edition, Vol. 18, pp. 443-478, J. Wiley 1982). The physical properties of such "polyblends" generally represent a compromise, which can mean an overall improvement as compared with the properties of the individual polymers. In these situations, multi-phase polymer mixtures have achieved much greater commercial significance than compatible mixtures (See Kirk-Othmer, loc. cit., p. 449.)
Multi-phase and compatible mixtures must therefore be kept strictly separate with regard to both their physical properties and their properties which are relevant for application technology, especially their optical properties (transparency, clarity, etc.). As already explained, a lack of compatibility often sets narrow limits for mixing plastics with the goal of thereby achieving an improved overall spectrum of properties. However, the state of the art does not offer any teaching to assist in finding the compatible polymer mixtures demanded by technology.